Art. iV.] . Herrick, Geology of Nm Mexico, §7 
rhyolite. The latter rises to the height of several hundred feet 
above the top of the lime only to drop away rapidly to the west. 
At a point some two or three miles further south a section 
across the axis above desribed indicates that there was much 
less of igneous outpour but the disturbance is particularly well 
shown as also the metamorphism of the acid member. The 
diagram (Plate XI, Fig. 5) illustrates the situation. 
Ideal Section through the axis of uplift south of Limitar 
mountain. i. Trachyte crater. 2. Laminated margin of trach- 
yte. 3. Porphyry about the margins. 4. Brecciated contact 
zone. 5. Massive limestone. 6. Shale with Productus cora. 
7. Quartzite (20 feet). 8. Shaly limestone with Spirifer came- 
rata. 9. Quartzite passing into the next. 10. Mica and horn- 
blende schist with quartzite bands and phases. 1 1 . Granite. 
13. Diorite intrusive (paramorphic). 14. Talus conglomerate 
in or near the crater. 
3 . 
MOUNT MAGDALENA AND THE BASIC ERUPTIVES OF THE MAGDA- 
LENA DISTRICT. 
With Plate XII. 
The general geological conditions of the Magdalena moun- 
tains formed the subject of an earlier paper to which reference 
is made throughout the following paragraphs.^ The present 
paper is devoted to an area immediately adjoining the range on 
the north and west. It will be recalled that the Magdalena 
mountains form a compact range extending nearly north and 
south for a distance of about twenty-five miles and separated 
from the Rio Grande at the north by the Socorro range. The 
distance from the river is from fifteen to twenty miles. The 
mountains rise rather abruptly from the plain some three thou- 
sand feet or to the elevation of ten thousand feet above tide. 
Its northern portion is formed along a fault line extending from 
^ The Geology of a Typical Mining Camp in New Mexico. American Ge- 
ologist, Vol. XIX, No. 4. 
